24LC024 datasheet(6/30 Pages) MICROCHIP

6 / 30 page

24AA024/24LC024/24AA025/24LC025

DS21210M-page 6

4.0

BUS CHARACTERISTICS

The following bus protocol has been defined:

• Data transfer may be initiated only when the bus

is not busy.

• During data transfer, the data line must remain

stable whenever the clock line is high. Changes in

the data line while the clock line is high will be

interpreted as a Start or Stop condition.

Accordingly, the following bus conditions have been

defined (Figure 4-1).

4.1

Bus Not Busy (A)

Both data and clock lines remain high.

4.2

Start Data Transfer (B)

A high-to-low transition of the SDA line while the clock

(SCL) is high determines a Start condition. All

commands must be preceded by a Start condition.

4.3

Stop Data Transfer (C)

A low-to-high transition of the SDA line while the clock

(SCL) is high determines a Stop condition. All

operations must be ended with a Stop condition.

4.4

Data Valid (D)

The state of the data line represents valid data when,

after a Start condition, the data line is stable for the

duration of the high period of the clock signal.

The data on the line must be changed during the low

period of the clock signal. There is one bit of data per

clock pulse.

Each data transfer is initiated with a Start condition and

terminated with a Stop condition. The number of the

data bytes transferred between the Start and Stop

conditions is determined by the master device and is,

theoretically, unlimited (though only the last sixteen will

be stored when performing a write operation). When an

overwrite does occur, it will replace data in a first-in

first-out fashion.

4.5

Acknowledge

Each receiving device, when addressed, is required to

generate an acknowledge after the reception of each

byte. The master device must generate an extra clock

pulse, which is associated with this Acknowledge bit.

The device that acknowledges has to pull down the SDA

line during the acknowledge clock pulse in such a way

that the SDA line is stable low during the high period of

the acknowledge-related clock pulse. Of course, setup

and hold times must be taken into account. A master

must signal an end of data to the slave by not generating

an Acknowledge bit on the last byte that has been

clocked out of the slave. In this case, the slave must

leave the data line high to enable the master to generate

the Stop condition (Figure 4-2).

FIGURE 4-1:

DATA TRANSFER SEQUENCE ON THE SERIAL BUS CHARACTERISTICS

FIGURE 4-2:

ACKNOWLEDGE TIMING

Note:

The 24AA024/24LC024/24AA025/24LC025

does not generate any Acknowledge bits if

an internal programming cycle is in prog-

ress.

(A)

(B)

(C)

(D)

(A)

(C)

SCL

SDA

Start

Condition

Address or

Acknowledge

Valid

Data

Allowed

to Change

Stop

Condition

SCL

123

Transmitter must release the SDA line at this point allowing

the Receiver to pull the SDA line low to acknowledge the

previous eight bits of data.

Receiver must release the SDA line at this

point so the Transmitter can continue

sending data.

SDA

Acknowledge

Bit

Data from transmitter

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